Responses of Carbon Isotope Composition of Common C₃ and C₄ Plants to Climatic Factors in Temperate Grasslands

Investigating relationships between climatic factors and plant δ13C of both C3 and C4 plants simultaneously is critical for accurately predicting the effects of climate change on plant ecophysiology and ecosystem functioning and reconstructing past vegetation and climate conditions. We selected common C3 and C4 plants in temperate grasslands in Inner Mongolia, China, i.e., Stipa spp., Carex spp., Leymus chinensis and Cleistogenes spp., and investigated the relationships between climatic factors and plant δ13C of each genus/species. The results showed that precipitation, especially growing season precipitation (GSP), was the dominant factor affecting plant δ13C in this region. For C3 plants, there were significantly negative relationships between precipitation and plant δ13C. For C4 plants, plant δ13C of Cleistogenes spp. firstly increased, then decreased with precipitation at a breakpoint GSP 204.84 mm. Our findings emphasize that C4 plant δ13C is sensitive to precipitation, but responses are species-specific and environment-specific, and suggest that C4 plant δ13C can be used as a proxy for water use efficiency (WUE), but care should be taken in evaluating WUE. Moreover, our findings provide basic information for accurately predicting the effects of climate change on ecosystem structure and function and reconstructing past vegetation and climate conditions from bulk materials in arid and semiarid regions